This invention relates to load handlers which mount on lift truck carriages. In one aspect, the invention relates particularly to a load handler having a fork positioner which can be attached to an existing lift truck carriage, or incorporated as original equipment in a newly-manufactured carriage. In a separate aspect, the invention relates to a wireless fluid power function selector for multifunction load handlers of different types, which may include fork positioners, push-pull attachments, load clamps or other types of load manipulators.
Fork positioners actuated by pairs of hydraulic cylinders, motor-driven screws, or the like represent one type of load handler used extensively on fork-supporting lift truck carriages. Most of these fork positioners are furnished as integral components of a carriage, often in combination with a side-shifting function which enables the carriage to be moved transversely so as to side-shift the forks in unison. Some detachably-mountable fork positioners have been provided in the past, such as those shown in U.S. Pat. Nos. 4,756,661, 4,902,190 and 6,672,823, to enable existing lift truck carriages without fork-positioning capability to be provided with such capability. However such detachably-mounted side-shifters have in the past increased the dimensions of the lift truck carriage, either horizontally as shown in U.S. Pat. No. 4,756,661 which reduces the load-carrying capacity of a counterbalanced lift truck by moving the load forward, or vertically as shown in U.S. Pat. Nos. 4,902,190 and 6,672,823 which impairs the lift truck operator's visibility over the top of the carriage.
Many types of load handlers have multiple separately-controllable fluid power functions. Most of these functions require bidirectional, reversible actuation. Examples of such load handlers include side-shifting fork positioners, side-shifting push-pull attachments, side-shifting and/or rotational load clamps having either parallel sliding clamp arms or pivoting clamp arms, and other types of fluid power-actuated multi-function load handlers. Normally, the foregoing types of load handlers are mounted on a load carriage which is selectively raised and lowered on a mast of an industrial lift truck. Multiple fluid control valves are often provided in the lift truck operator's compartment to separately regulate each of the multiple fluid power functions of the load handler. In such cases, four or even six hydraulic lines must communicate between the lift truck and the load handler to operate the multiple bidirectional functions. To avoid the necessity for more than two hydraulic lines, it has long been common to provide only a single control valve in the operator's compartment connected to a single pair of hydraulic lines extending between the lift truck and a multi-function load handler. In such case, one or more solenoid valves are mounted on the load handler controlled by electrical wires routed between the lift truck and the load handler so that the operator can electrically select which load handler function will be actuated by the single pair of hydraulic lines. However, routing the electrical wires over the lift truck mast to a vertically movable load handler requires exposure of the wires and their connectors to significant hazards, wear and deterioration, resulting in breakage, short-circuiting, corrosion and other problems which require relatively frequent replacement and downtime. Moreover, lift truck electrical systems range from twelve to ninety-six volts, requiring a variety of special coils for the solenoid valves.
In other types of industrial work equipment, it has been known to control one or more remote solenoid valves by means of a radio transmitter controlled by the operator, which controls the solenoid valve(s) by sending signals to a remote receiver, as shown for example in U.S. Pat. Nos. 3,647,255, 3,768,367, 3,892,079, 4,381,872, 4,526,413, and 6,662,881. However, these control systems are generally not compatible with the special requirements of lift truck-mounted load handlers with respect to minimizing the size and electrical power demands of such systems, and maximizing the safety thereof. For example, their lack of two-way wireless communication between the transmitter and receiver limits the functionality, reliability and safety of their working components.